Glass seal for a turbine



1968 D. G. MILLER 3,398,931

GLASS SEAL FOR A TURBINE Filed Sept. 9, 1966 INVENTOR.

, ATTORNEY advbah fro ye //7z2 /er v United States Patent "ice 3,398,931 GLASS SEAL FOR A TURBINE Donald G. Miller, Indianapolis, Ind., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Sept. 9, 1966, Ser. No. 578,285 9 Claims. (Cl. 253-39) This invention relates to turbine engines, and more particularly to a glass seal for a turbine and a method for making glass seals.

Generally, a turbine includes a rotor which carries rows of outwardly extending rotor blades and a compressor housing which carries corresponding rows of stationary vanes arranged in abutting relationship which are commonly referred to as stator vanes. Gas leakage through the clearance spaces existing between the abutting surfaces of the stationary stator vanes is a primary source of energy loss in turbine engines. These clearance spaces between the stator vanes are essential in order to compensate for thermal expansion, warpages and elastic deformations of the metal vanes.

It is a basic object of this invention to increase the efficiency of gas turbines by reducing gas leakage between the abutting surfaces of the stator vane segments.

It is another object of this invention to provide sealing means for the clearance space separating the stator vane segments.

It is still another object of this invention to design specific sealing means for stationary turbine parts which are operated at temperatures between 1700 and 2000 F.

These and other objects are accomplished by individually coating the abutting side surfaces at the ends of the stator vane segments with a thin layer of glass. These stator vane segments are then assembled in the turbine in the normal manner. At operating temperatures the abutting glass coatings soften sufliciently to flow together and form a viscous glass mass therebetween completely sealing the clearance space between the abutting side faces. The glass coating is sufiiciently yieldable to provide for thermal expansion and contraction of the metal parts during thermal cycling.

Further objects and advantages of the present invention will be apparent from the following detailed description, reference being had to the drawings wherein the preferred embodiment of the present invention is clearly shown.

In the drawings:

FIGURE 1 is an elevational view of a row of stator vanes;

FIGURE 2 is a cross-sectional view of the abutting sides at the ends of the stator vanes after installation;

FIGURE 3 is a cross-sectional view of the abutting sides at the ends of the stator vanes during the operation of the turbine engine; and

FIGURE 4 is a perspective view of a stator Vane segment.

Referring now to the drawings, FIGURE 1 is an elevational view of a portion of a row of individual stator vane segments assembled together in the conventional manner as found in the gas turbine engine. As shown in FIGURE 4, an individual stator vane segment consists of a vane 12 having an upper end 14 wherein the end 14 has two faces 16 and 18 on one side thereof. The lower end 20 of the stator vane has two side faces 22 and 24 on the same side thereof. Side faces 16 and 18 at end 14 and side faces 22 and 24 at end 20 abut side faces 28 and 30 and faces 32 and 34 respectively on the adjacent stator vane section as shown in FIGURE 1. In accordance with the practice of this invention, the leakage between abutting side faces 16 and 28, 18 and 30, 22 and 32 and 24 and 34 is eliminated by the presence of a vis- 3,398,931 Patented Aug. 27, 1968 cous glass seal thereby increasing the efliciency of the gas turbine engine.

As shown in FIGURE 2, side face 16 is coated with a glass coating 38. Similarly, side face 28 is coated with a layer of glass 36. In the same manner the other abutting side faces 18, 30, 22, 32, 24 and 34 of the adjoining vane segments are also coated with a layer of glass. The coated vane segments are then assembled in a row abutting each other in the conventional manner. The thin coating of glass is yielding enough to permit normal installation, the glass flexibly yielding when resistance from an adjoining vane segment is encountered. The thickness of the glass coating on the side face may vary from two to ten mils depending on the size of the clearance space. The thickness of the glass coating in the preferred embodiment is 5 to 8 mils. Although the preferred method involves individually coating the side faces of the vane segment with a glass coating and then assembling the individual segments in a row abutting each other, the glass may be applied into the clearance space separating the vane segment side faces after the vane segments have been assembled in a row.

The composition of the glass frit used to make the glass coating may vary over a wide range depending upon the temperature to which the glass coating will be subjected. In the preferred embodiment, where the side faces of the stator vane segments are subjected to a temperature in the range of 1700 to 2000 F., the composition of a preferred glass frit is 59 weight percent silicon oxide, 15 weight percent calcium oxide, 6 weight percent sodium oxide and 20 weight percent chromium oxide. Glass frits of this type which are satisfactory in a temperature range of 1700 to 2000 F. contain 50 to parts silicon oxide, 10 to 20 parts calcium oxide, 2 to 10 parts sodium oxide and 10 to 30 parts chromium oxide. As previously mentioned, the composition of the glass frit to be used in the practice of this invention is determined by the temperature at which the glass becomes fluid, in other words, the glass used in the clearance space between the stator vane segments which are exposed to temperatures in the range of 1700 to 2000 F. must be soft enough and viscous enough to flow slowly and fill the clearance space. If the glass is not viscous enough between 1700 to 2000 F., it will not be acceptable in the application. Similarly, if the glass is not soft enough to flow at this temperature, it is not acceptable. The composition of the glass must be such that at operating temperatures the abutting glass coatings soften sufficiently to flow together and form a viscous glass mass therebetween completely sealing the clearance space between the abutting side faces. This composition is melted and the resultant mixture milled to a powder having a particle size in which the diameter is less than 20 microns. It is Well known in the art that homogeneous aqueous glass suspensions can be made when the glass powder particle size is 20 microns or less in diameter. A homogeneous aqueous glass suspension containing about weight percent glass is made and applied by spraying, dipping, or by vibration techniques to each side face of the vane segments. The applied coating is then fused at 1650 F. for five minutes. At room temperature, the thin glass coating on the side faces is relatively hard, but it is sufficiently flexible under pressure to permit normal installation in forming a row of adjacent vane segments.

During the time the turbine engine warms up to a temperature between 1700 to 2000 F., the glass coating softens sufficiently to flow slowly into the clearance space 40 separa ing the two abutting glass coatings as shown in FIGURE 2 to form a continuous viscous glass mass 42 which seals space 40, as shown in FIGURE 3.

As the temperature of the turbine engine increases to the operating temperature of 1700 F. to 2000 F., the

viscous glassmass 42 whichseals the clearance space would yield sufliciently to permit the side faces 16 and 28 to expand into the clearance space 40 so as not to produce compressive stresses in the stator vane segments. At operating temperatures, the soft, highly viscous glass mass seals the clearance space to prevent gas leakage thereby increasing the efliciency of the gas turbine. When the turbine is shut down and cooled, it has been observed that some of the vane segments remain bonded together by the glass seal 42 but can be easily separated. Even though the glass seal 42 may fracture or crack in the clearance gap between the side faces of the vane segments as a resultof a rapid cool-down, the glass seal will be reformed as soon as the engine temperatures become high enough to cause the glass mass to flow. The coatings may be removed, if desired, by vapor blasting and may be repaired by the application of a new glass slurry and refiring.

Although, as described above, the seal and method of this invention has particular utility in completely sealing the clearance space between the abutting side faces of a stator vane segment in a turbine, it is obvious that this seal may be readily employed to other stationary metal parts subjected to thermal cycling which abut each other and which are separated by a small clearance space. In these cases, as indicated above, the composition of the glass would depend upon the operating temperature of the coated metal parts.

While the invention has been described in terms of a preferred embodiment, it is to be understood that it is not limited thereby except as defined in the following claims.

I claim:

1. A glass seal adapted to reduce gas leakage between abutting metal parts in a gas turbine at operating temperatures comprising a glass mass having a solftening temperature substantially the same as the temperature of the abutting metal parts under gas turbine operating conditions, said glass mass softening suificiently at these temperatures to form a viscous glass mass completely sealing the space between said abutting metal parts.

2. A glass seal adapted to reduce gas leakage between abutting stator vane segments in a gas turbine at temperatures in the range of 1700 to 2000 F. comprising a glass mass softening sufficiently in the temperature range of 1700 to 2000 F. to form a viscous glass mass completely sealing the space between said abutting vane segments.

3. A glass seal as described in claim 2 wherein said glass mass contains 50 to 75 parts silicon oxides, to 20 parts calcium oxide, 2 to 10 parts sodium oxide and 10 to 30 parts chromium oxide.

4. 'A turbine stator ring comprising a plurality of stator vane segments arranged in abutting relationship, and the abutting surfaces of said segments having a glass coating thereon, said glass coatings adapted to soften at gas turbine operating temperatures sufficiently to flow together to form an air-tight seal.

5. A turbine stator ring as described in claim 4 wherein said glass coating contains 50 to parts silicon oxide, 10 to 20 parts calcium oxide, 2 to .10 parts sodium oxide and 10 to 30 parts chromium oxide.

6. In a turbine stator ring the combination of abutting surfaces of stator vane segments and a glass coating on said surfaces, said glass coating softening at turbine operating temperatures to flow sufficiently to form a mass which completely seals the space between said side faces thereby reducing gas leakage therebetween.

7. A method for sealing the clearance space between abutting metal parts in a gas turbine comprising the steps of coating the abutting surfaces of said metal parts with a layer of glass, assembling the glass coated metal parts and operating said gas turbine, said glass layer softening sufiiciently from the heat generated by the operation of said gas turbine to flow together and seal the clearance space between said metal parts.

8. A method for sealing the clearance space between abutting metal parts in a gas turbine comprising the steps of forming a glass layer in said clearance space between the abutting surfaces of said metal parts and operating said gas turbine, said glass layer softening sufficiently from the heat generated by the operation of said gas turbine to flow together and to seal the clearance space between said metal parts.

9. A method for improving operating efficiency in a turbine engine having a multiplicity of stator vane segments arranged in abutting relationship, by applying a glass coating to the abutting surfaces of the stator vane segments, fusing the coating at an elevated temperature, assembling the cooperating vane segments so that the glass coated surfaces thereof are in touching relationship and operating said gas turbine, said glass coating softening sufiiciently from the heat generated by the operation of said gas turbine to flow together and seal the clearance spaces between said vane segments.

References Cited UNITED STATES PATENTS 2,742,224 4/1956 Burhans 253-77 EVERETTE A. POWELL, JR., Primary Examiner. 

1. A GAS SEAL ADAPTED TO REDUCE GAS LEAKAGE BETWEEN ABUTTING METAL PARTS IN A GAS TURBINE AT OPERATING TEMPERATURE COMPRISING A GLASS MASS HAVING A SOFTENING TEMPERATURE SUBSTANTIALLY THE SAME AS THE TEMPERATURE OF THE ABUTTING METAL PARTS UNDER GAS TURBINE OPERATING CONDITIONS, SAID GLASS MASS SOFTENING SUFFICIENTLY AT THESE TEMPERATURES TO FORM A VISCOUS GLASSMASS COMPLETELY SEALING THE SPACE BETWEEN SAID ABUTTING METAL PARTS. 